subscript/feature/number.js

Fast and tiny expression evaluator with minimal syntax.

import { lookup, next, skip, err, cur, idx } from "../src/parse.js"
import { PERIOD, _0, _E, _e, _9 } from "../src/const.js"

// parse number
const num = (a, _) => [, (
  a = +next(c => (c === PERIOD) || (c >= _0 && c <= _9) || (c === _E || c === _e ? 2 : 0))
) != a ? err() : a]

// .1
lookup[PERIOD] = a => !a && num()

// 0-9
for (let i = _0; i <= _9; i++) lookup[i] = a => a ? err() : num()